ec subtract

[Christian Grothoff]

Hohey!

Sounds like a question for libgcrypt hackers.  Extending the API to
make it trivial to invert a point would make sense IMO.


Happy hacking!

Christian

On 07/10/2014 07:14 PM, Markus Teich wrote:
> Heyho,
>
> for the ECBD I need to subtract two points on the curve (Z_{i+1} - Z_{i-1}). I
> found out[0], that I have to invert the y value of the second point to achieve
> this. However in libgcrypt (1.6.1) there seems to be no function, which achieves
> that easily[1]. Do I really have to use gcry_mpi_point_get, gcry_mpi_sub and
> gcry_mpi_point_set to invert the point?
>
> A gcry_mpi_ec_sub should definitely be supplied by the libgcrypt API.
>
> --Markus
>
>
> [0] http://crypto.stackexchange.com/questions/11316/subtracting-a-point-in-elliptic-curve-cryptography
> [1] https://www.gnupg.org/documentation/manuals/gcrypt/EC-functions.html


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